Spectrophotometric monitoring is not suitable to determine the end point of titration of:
(a)oxalic acid vs potassium permanganate
(b)iron(II) vs 1, 10-phenanthroline
(c)cobalt(II) vs eriochrome black T
(d)nickel (II) vs dimethylglyoxime
Answer
Answer: D ✓ checked by 4AB · confidence medium
The source book printed no answer; this one was worked out and checked — see the explanation.
Printed C; the DMG complex precipitates, which the question rules out.
Explanation
A spectrophotometric (photometric) titration needs a clear, homogeneous solution in which the analyte, titrant or product absorbs, so that the absorbance changes steadily up to the end point. (a) MnO₄⁻ is intensely coloured: once the end point is passed, excess permanganate raises the absorbance, so this titration is suitable. (b) Fe²⁺ and 1,10-phenanthroline form the intensely red ferroin complex (λmax ≈ 510 nm), so this one is suitable. (c) Co²⁺ forms a coloured complex with the dye eriochrome black T, so the absorbance change can be followed. (d) Ni²⁺ and dimethylglyoxime give an insoluble red precipitate of Ni(dmgH)₂. The turbid suspension scatters light, so absorbance cannot be measured meaningfully and spectrophotometric monitoring is not suitable. Answer: (d).